I've been contacted frequently over the past few months regarding the basis for false-positive results from rapid screen THC immunoassays. These inquiries are usually in the context of pre-employment and random urine screening, but occasionally arise from more unusual circumstances (Hugo, CO). I was asked yesterday about the potential for false positive THC results in newborns, and after looking into it, the answer surprised me. It turns out false-positives for THC are fairly common. Upon observing that follow-up screening by GC-MS failed to verify the initial positive immunoassay test result in newborns, a team of social workers, care providers, hospital staff, and laboratory personnel at UNC - Chapel Hill investigated this issue. They determined that THC immunoassays react with, among other things, non-THC components of baby soap, including cocamidoprophyl betaine, polyquaternium 11, PEG 80 and sorbitan laurate, and numerous other compounds, thus leading to an unusual number of false-positives during newborn drug screening.

Negative Consequence of False-PositivesAs legal cannabis becomes more widely available across the United States, it becomes even more important to be aware of the potential for false-positive results in many areas ranging from commonplace employment drug testing, to motor vehicle operation, and now to newborn drug screening. The negative legal, economic, and social consequences of false-positives are considerable and too lengthy a topic to go into here.

False-Positives in Newborns Positive immunoassay results are confirmed or refuted with more sophisticated methods such as GC-MS, but a considerable amount of time (often days) may elapse between the preliminary result and verification. In that interim period there is potential for involvement by child protective services and allegations of child abuse. Given the seriousness of these consequences, it is incumbent on care providers and laboratory personnel to be aware of the limits of preliminary immunoassay screening and to consider secondary testing and confirmation prior to initiating costly and possibly unnecessary interventions.

CreditsShout out to the team of social workers, care providers, hospital staff, and laboratory personnel from UNC-Chapel Hill who took the time to work out this puzzle.